Method of conditioning and all-position mercury switch



Dec. 31, 1963 w. D. O'BRIEN ETI'AL 3,116,334

METHOD OF CONDITIONING AN ALL-POSITION MERCURY SWITCH Filed Nov. 2, 1961FIG.

W. D. OB/P/E N INVENTORS a E POL LARD, JR,

CMM

ATTORNEY United States Patent 3,1165% ME'LHUD 0F QllNDl'llQh-IING ANALLPOSHTIUN MERCURY SWHTCH ll illiain l). (lillrlen, New York, NJY andCharles E. Pollard, .lr., Hoholtus, ML, assignors to Bell Telephonellahorutories, incorporated, New York, N.Y., a corporation of New YorkFiled Nov. 2, 1961, Ser. No. 149,691 4 Claims. (Cl. 200-112) Thisinvention relates to sealed reed switches having \vetted contacts and tomethods of making them. More particularly, it is concerned with sealedreed, mercury switches that may be operated in any attitude, that is,allposition switches.

Mercury switches, in general, have enough mercury in them to make theattitude of the switch housing significant; for example, in the tiltingtype switch, the attitude determines whether the switch is on or oil. Inthe sealed reed, mercury-wetted-contact type, as disclosed in Patent2,868,926 to C. E. Pollard, In, issued January 13, 1959, the switch mustbe used in a vertical, or nearly vertical, position so that the freemercury will not cause a short circuit by flowing between the contacts.

The present invention involves a sealed, mercurywetted-contact reedswitch with no excess mercury to ilow around, whereby it may be used inany attitude or position.

in the usual mercury, reed type switch, as disclosed in the notedPollard patent, there is mercury in the reservoir or cup and also on thecontacts and on the swinger which projects from the cup. The swinger isusually provided with a plurality of longitudinal grooves to aid inconduct ing mercury from the cup to the contacts and for present ing agreater storage surface than a smooth swinger.

The mercury which adheres to or wets the contacts and the swinger bysurface tension is gradually dissipated at the contacts, minute dropletsbeing lost during switch operation. Thus, the reservoir is used so thatreplacement mercury is available. However, such a switch, as has beennoted, is limited as to the position in which it may be properly used.

Applicants have solved the problem of making a sealed reed switch withmercury-wetted contacts and operable in any position by having in theswitch envelope or housing only sufficient mercury to wet the swingerand the contacts.

Such a switch might be made by sealing within the envelope 1016 thanenough mercury to wet the switch ports, activating the switch, andthereafter unsealing the envelope, removing the excess mercury, and thenrescaling the envelope. The operation called activating comprises theassembly and agitating it to suitably coat the contacts and the swingerwith mercury. This way or making a switch appears to be simple, butcarrying it out properly is the first concern of the present invention.

it" too much mercury is removed from the switch parts, the life of theassembly is reduced more than can be tolerated for many uses. A switchin accordance with this invention, proerly made, may be good for aboutone million operatic. s, but this would be drastically reduced if toomuch mercury were removed. Moreover, once the right amount has beendetermined, the question of reproducibility arises; that is, will eachswitch be the same as every other switch? There also arises the questionor contamination during mercury removal.

One of the usual ways of making a mercury switch is to introduce mercuryinto the envelope in which the reeds are mounted, to evacuate and fillthe envelope with a suitable gas, say hydrogen, and then to seal theenvelope. it has been iound, as set forth in Patent 2,732,459

" ice to C. E. Pollard, In, that the addition of a small amount ofcopper to the mercury avoids contact sticking under certaincircumstances. Tin, as well as copper, may be added with benefit, inaccordance with Pollard Patent 3,018,354, issued January 23, 1962, onapplication Serial No. 848,628, filed October 22, 1959. The added metalsmay be put into the switch envelope prior to the introduction of themercury.

In order to make a good switch, all of the internal parts and theintroduced materials must be cleaned and be kept clean. This is nocontinuing problem with the usual switch after it has been sealed, butto make the present switch, unsealing with its attendant chances ofcontamination appears necessary. One source of contamination that isparticularly troublesome is tin that has oxidized due to contact withthe atmosphere.

An object then of this invention is to take advantage of some of theproperties of sealed reed, mercury switches, namely, mercury wetting ofcontacts, and, at the same time, eliminate one of its undesirablecharacteristics, namely, limited position of use. In other words, anobject is to make a sealed reed switch having mercury-wetted contactsbut which is usable in any attitude, namely, an all-position switch.

One of the features of this invention resides in the means for andmethod of making a sealed reed mercury switch having therein onlysutlicient mercury to properly wet tie contacts and the contact swinger.

Other and further objects and features of this invention will appearmore fully and clearly from the following description of an exemplaryembodiment of the switch and of the method of making it, as illustratedin the appended drawings, in which:

FIG. 1 shows a longitudinal section of a switch in accordance with thisinvention;

FIG. 2 shows the switch of FIG. used during its manufacture; and

FIG. 3 shows diagrammatically a centrifuge for performing one of theprocess steps on the FIG. 2 assembly.

As shown in FIG. 1, the switch comprises a housing ltl which may be asection of glass tubing. A pair of fixed contacts ll and 12 are securedin spaced relation by means of the terminals l3 and 14, respectively.These terminals are sealed through one end of the housing it A movablecontact carrier or swinger 15 projects between the fixed contacts and 12and may be biased 1 with attachments llEL either of them or neither, asrequired, by the way the swinger is initi ly fixed in the housing. Theswinger is attached to a tab 16 which, in turn, is secured to andprojects from the tubulation 1'). Besides mounting the swinger, thetabulation i7 is, as is well known, in communication with the interiorof the housing. The tube or tubulation It? may be made or" a suitablemetal or alloy, such as nickel-iron. his tube is flared at its innerend, and its lip and the glass of the housing are aired so that there isno pocket to interfere with egress of mercury.

As may be noted in PEG. 1, the tube 1? is sealed at It will be noted,however, by reference to FIG. 2 that the making of the switch thetribulation 17 e ads to and is sealed into an auxiliary housing 21 whichmay also be of glass. The auxiliary housing also ha tribulation at itsouter end.

he switches are made up with their attachments, as in FIG. 2. Email bitsor slugs of copper, and of tin, if used, are introduced into thehousing. A quantity of mercury greater than that need for the finishedswitch is then added. The assembly is then evacuated and filled with asuitable gas, such as hydrogen, by way of the tube 22, the housing 21,and the tube 17. The tube is then closed as by welding at 23 (see FIG.3).

The next step is to activate the switch which, viously noted, comprisesthe application of heat agitation of tie housing. A suitable temperatureis 320 degrees Centigrade. The activation may he a vibration of smallamplitude, for example, 32 of an inch, at about 60 vibrations per secondin a longitudinal direction. The switch is held in a vertical positionwith the contacts down, and the mercury in which the free end of theswinger and the fixed contacts are immersed travels up the swinger tocoat it completely. This small amplitude vibration avoids splashing ofmercury with its attendant difiiculties. One result of splashing mightbe to Wet the inside of the connecting tube with the mercury-tin-coppersolution. The tin and copper, which could not be easil removed later,would interfere with later welding of the tube to seal the switch.

The manufacturing assembly is clamped in a centrifuge, as in H6. 3, forthe removal of excess mercury. The centrifuge may be a tube secured to arotatable shaft 31 and having a pin, screw, or other means for retainingthe switch during rotation. For example, the screws 32 may be used. Ithas been found that rotation for about 30 seconds at a speedcorresponding to a centrifugal acceleration about 30 times that ofgravity serves the purpose. For noted switch, about 750 revolutions perminute is suitable, with the switch contacts at about two inches fromthe center of rotation. This speed and radius amounts to an accelerationof about 32.5 gs; up to about 35 gs appears to be reasonable. In otherwords, the range is about 36 to 35 gs for satisfactory manufacture.

After removal of the excess mercury to the auxiliary housing 21, thetubulation 17 is sealed at an intermediate point, as indicated by thearrow 25 in FIG. 2. This is the seal 18 shown in FIG. 1.

The sealing may be, and advantageously is, by welding. In order to besure that there is no condensed mercury vapor in the tube 17 at thesealing zone, heat is applied to the tube before welding to evaporatethis mercury; otherwise, the weld might not be good.

As previously indicated, the switch made in accordance with thisinvention appears to be capable of about one million operations beforethe mercury wetting becomes ineffective. The mercury that is on thecontacts and the swinger will remain there unless subjected to anacceleration greater than the 30 to 35 gs used during its manufacture.

What is claimed is:

1. The method of conditioning an all-position sealed reed, mercuryswitch by storing mercury on the contacts and the swinger only, thatcomprises including a reservoir in the tribulation that normally extendsfrom the switch envelope during manufacture, injecting into the envelopean excess of mercury, evacuating and sealing the tubulation at a pointto include the reservoir, activatas preto and the ing the switch byagitating and heating it to cause mercury to adhere to the contacts andthe swinger, transferring the remaining mercury to the reservoir bycentrifuging at a speed to attain a radial acceleration 30 to 35 timesthe acceleration of gravity, sealing the tu'oulation between theenvelope and the reservoir, and severing the tabulation to remove thereservoir.

2. The method of conditioning all-position sealed reed, mercury switchby storing mercury on the contacts and the swinger only, that comprisesincluding a reservoir in the tribulation that normally extends from theswitch envelope during manufacture, injecting into the switch envelopean excess of mercury, evacuating and sealing the tabulation at a pointto include the reservoir, activating the switch by agitating and heatingit to cause mercury to adhere to the contacts and the swinger, transingthe remaining mercury to the reservoir by centrnuging at a speed toattain a radial acceleration 32.5 times the acceleration of gravity,sealing the tribulation ,veen the envelope and the reservoir, andsevering the tLlOtllZliiOfl to remove the reservoir.

The method of conditioning an all-position sealed reed, mercury switchby storing mercury on the centre the sger only, that comprises includinga reservoir in the tribulation that normally extends from the switchenvelope during manufacture, injecting into the envelope by way of thereservoir an excess of mercury, evacuating and sealing the tribulationat a point to include the reservoir, activating the switch to causemercury to adhere to the contacts and the swinger, transferring theremaining mercury to the reservoir by centrifuging at a speed to attaina radial acceleration 30 to 35 times the acceleration of gravity,sealing the tabulation between the envelope and the reservoir, andsevering the tubulation to remove the reservoir.

The method of conditioning an all-position sealed reed, mercury switchthat includes an envelope, fixed contacts, a contact swinger, and atubulation, by storing mercury on the contacts and the swinger only,that comises temporarily including a reservoir in the tubulation,injecting into the envelope an excess of mercury, evacuating and sealingthe tubulation at a point to include the reservoir, activating theswitch by agitating the heating it to cause mercury to adhere to thecontacts and the swinger, transferring the remaining mercury to thereservoir by centrifuging at a speed to attain a radial acceleration 30to 35 times the acceleration of gravity, sealing the tabulation betweenthe envelope and the reservoir, and severing the tabulation to removethe reservoir.

References Cited in the file of this patent UNITED STATES PATENTSPollard July 20, 1948 Brown et al. Nov. 6, 1956

1. THE METHOD OF CONDITIONING AN ALL-POSITION SEALED REED, MERCURYSWITCH BY STORING MERCURY ON THE CONTACTS AND THE SWINGER ONLY, THECOMPRISES INCLUDING A RESERVOIR IN THE TUBULATION THAT NORMALLY EXTENDSFROM THE SWITCH ENVELOPE DURING MANUFACTURE, INJECTING INTO THE ENVELOPEAN EXCESS OF MERCURY, EVACUATING AND SEALING THE TUBULATION AT A POINTTO INCLUDE THE RESERVOIR, ACTIVATING THE SWITCH BY AGITATING AND HEATINGIT TO CAUSE MERCURY TO ADHERE TO THE CONTACTS AND THE SWINGER,TRANSFERRING THE REMAINING MERCURY TO THE RESERVOIR BY CENTRIFUGING AT ASPEED TO ATTAIN A RADIAL ACCELERATION 30 TO 35 TIMES THE ACCELERATION OFGRAVITY, SEALING THE TUBULATION BETWEEN THE ENVELOPE AND THE RESERVOIR,AND SEVERING THE TUBULATION TO REMOVE THE RESERVOIR.